Answer: A dynamic character
"a dynamic character also undergoes changes throughout the narrative, due to conflicts he encounters on his journey. A dynamic character faces trials and tribulations, and takes time to learn from his encounters, his experiences, and his mistakes, as well as from other characters."
- From <u><em>https://literarydevices.net/dynamic-character</em></u>
Metaphor; its showing how that rack was moving alot-something like how a teeter totter would look had someone been playing on it. it was comparing the rack to a teeter totter